A bypass valve can be used to maintain a constant pressure drop across the inlet and outlet of a metering valve, such as a metering valve that forms a part of a fluid pressure system. Generally, a bypass valve comprises a valve piston adapted to reciprocate within a valve sleeve. The bypass valve references the differential pressure across the metering valve. The force due to the differential pressure is countered by a linear compression spring. This results in proportionality between the metering valve's differential pressure and the bypass valve's position. The valve sleeve also includes a low pressure bypass outlet port for bypassing excess fluid from the high pressure side of the system to a bypass line back to the inlet of a positive displacement pump.
An increase in the pressure upstream of the metering valve or a decrease in the pressure downstream of the metering valve will tend to open the bypass return port. A decrease in the pressure upstream of the metering valve or an increase in the pressure downstream of the metering valve will tend to close the bypass return port. Thus the bypass valve adjusts the flow returned to the high pressure pump to maintain a constant differential across the metering valve.
As metered flow travels around the bypass valve and as returned flow enters and exits the bypass valve, radial loads are imparted on the valve piston. The radial loads are influenced by such factors as the geometry of the valve piston, the geometry of the valve sleeve, the flow patterns of both the metered and returned flow paths, and the varying velocity and pressure levels of the fluid within the bypass valve sleeve. The resultant piston side loads negatively impact the steady state as well as the dynamic performance of the bypass valve.
New developments in engine design have been accompanied by a demand for increased fuel flow and higher temperature and pressure levels. These changes in fuel system boundaries create a broader and more severe environment which system hardware, including such components as bypass valves, must dynamically respond without degrading. In particular, the changes in bypass valve environmental conditions create a higher likelihood for elevated friction as a result of broad pressure and flow ranges and the increase in valve size to accommodate these broad flow and pressure ranges.